Has there ever truly been a "Christian civilization?" I would question that very premise, because we know that satan is the god of this world and that he roams around like a prowling lion, seeking whom he can devour. Between people's own innate sin nature and the continual interference from the bad guy and his minions, it's a constant fight. So yeah, people are sinners and some people really, really like to sin. Thankfully, some will eventually seek God and when they do, they will find Him.